Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$14.36	6.839%	$15.3421	$15.34	$15.35	$15.30
Purchase #2	$191.43	10.693%	$211.8996	$211.90	$211.90	$211.90
Purchase #3	$191.80	12.773%	$216.2986	$216.30	$216.30	$216.30
Purchase #4	$20.31	6.395%	$21.6088	$21.61	$21.60	$21.60
Purchase #5	$108.75	10.426%	$120.0883	$120.09	$120.10	$120.10
Purchase #6	$45.48	7.163%	$48.7377	$48.74	$48.75	$48.70
Purchase #7	$78.66	13.601%	$89.3585	$89.36	$89.35	$89.40
7 purchase totals =	$650.79		$723.3336	$723.34	$723.35	$723.30